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RE: IPv6 prefix lengths - how long?

"Manfredi (US), Albert E" <albert.e.manfredi@boeing.com> Tue, 11 June 2019 01:20 UTC

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From: "Manfredi (US), Albert E" <albert.e.manfredi@boeing.com>
To: Mark Smith <markzzzsmith@gmail.com>
CC: 6man WG <ipv6@ietf.org>
Subject: RE: IPv6 prefix lengths - how long?
Thread-Topic: IPv6 prefix lengths - how long?
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Date: Tue, 11 Jun 2019 01:20:24 +0000
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We’ve been around and around on this. Today’s reality is that households and devices are being provided, in many cases, with only a /64. Therefore, unless the households or devices are happy with a flat address space inside their /64, prefix, they would need to be assigned more /64 prefixes.

In many cases, I’d say universally actually, users prefer to architect their systems as they see fit, without having to involve new requests to their ISPs. IPv4 taught us to appreciate the flexibility of CIDR. IMO, I’d leave it wide open, the prefix length, and many RFCs not related to ULA, link local, or SLAAC already allow this. In fact, even SLAAC can easily be made to accommodate various prefix/IID lengths, if it should ever come to that.

(Sorry for top posting.)

Bert


From: ipv6 <ipv6-bounces@ietf.org> On Behalf Of Mark Smith
Sent: Monday, June 10, 2019 20:32
To: Templin (US), Fred L <Fred.L.Templin@boeing.com>
Cc: 6man WG <ipv6@ietf.org>
Subject: Re: IPv6 prefix lengths - how long?


On Tue., 11 Jun. 2019, 02:54 Templin (US), Fred L, <Fred.L.Templin@boeing.com<mailto:Fred.L.Templin@boeing.com>> wrote:
Two points I pulled out of the many points that were made were that 1) prefixes that are
overly long can be trivially enumerated by an attacker, and 2) prefixes should be aligned
on nibble boundaries.

I really resonate with point 1), and with Host Address Availability (RFC7934) we see that
it is good to allow hosts (nodes) to configure many IPv6 addresses - perhaps even very
many. I agree with the points that there are already vast numbers of /64s available for
delegation, and /64 has many nice properties including RFC7934 support and intractable
address enumeration. But, if we want to go longer than /64


Why do we want to go longer than /64?

The IPv6 address space is 2^96 times, or about 73 billion billion times larger than IPv4s.

Plenty of people have done the maths to show that we are not going to run out of IPv6 addresses.

Just a few months ago Brian worked out that every grain of sand on Earth could have its own /64, and from memory, that was just within 2000::/3.

For a technical field, I'm becoming more and more amazed at how many people trust their intuition completely ("IPv4 ran out in a few decades so IPv6 will too"), rather than saying to themselves, "my intuition may be correct, do the facts support it?".

It's not engineering if people rely on intuition, because ever now and then things are counter-intuitive.


and still satisfy those
properties, how long would that be - /96?

Point 2) I am not as sure on. Why is it important for prefixes to land on even nibble
boundaries? I can easily delegate a /63 today for example, and I don't see anything
wrong with that. Are we saying that that should be disallowed?

Fred
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